Standard entropies of $X_2$, $Y_2$ and $XY_3$ are 60, 30 and 50 JK$^{-1}$ mol$^{-1}$ respectively. For the reaction $\frac{1}{2}X_2 + \frac{3}{2}Y_2 \rightleftharpoons XY_3$, $\Delta H = -30$ kJ. To be at equilibrium, the temperature should be: